Method and system for mobility management in communication networks

ABSTRACT

In one embodiment, a gateway label edge router (G-LER) receives a packet destined for a mobile domain that comprises a vehicle label edge router. The G-LER identifies, from among a plurality of primary domains, a particular primary domain that currently has a label switched connection with the mobile domain. The label switched connection connects the vehicle label edge router of the mobile domain and a cluster label edge router of the particular primary domain. The G-LER sends the packet to the cluster label edge router of the particular primary domain for transmission to the vehicle label edge router via the label switched connection. The G-LER tracks when the vehicle label edge router of the mobile domain establishes a new label switched connection with a second cluster label edge router of a different primary domain in the plurality of primary domains than that of the particular primary domain.

RELATED APPLICATION

This application is claims priority to EP Appl. No. 19206014, filed Oct.29, 2019, entitled METHOD AND SYSTEM FOR MOBILITY MANAGEMENT INCOMMUNICATION NETWORKS, by Bisti et al., the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to communication networks and,more particularly, to mobility management in communication networkscomprising label switched networks.

BACKGROUND

Label switched networks are networks wherein data packets are forwardedon the basis of labels. A practical implementation of label switchingcould be based on Multiprotocol Label Switching (MPLS), which is anInternet Engineering Task Force (IETF) standardized protocol. Accordingto MPLS, data packets entering the network at one node, called ingress,are classified into a Forwarding Equivalence Class (FEC). All datapackets with a same FEC follow a same primary path (called LabelSwitched Path or LSP) to a destination node, called egress. The nodes ofthe network, including intermediate ones, take per-packet forwardingdecisions based on label Forwarding Information Base (FIB) tables.

Wireless communication in high-speed vehicular mobility scenarios posescomplex technical challenges across several layers of the ISO-OSI stack,including the physical layer (Layer 1), the data layer (Layer 2) and thenetwork layer (Layer 3). Unlike a stationary environment, where roamingis rare and deferred communication is tolerated, in high-speed vehicularmobility scenarios handoff is a certainty. Continuous reliable wirelessconnection with seamless handoff and sustained communication for smoothoperation is required. Moreover, as the train speed increases,communications between the train and infrastructure encounter majordifficulties of maintaining such high-quality communication and yetthere is no effective solution able to cope with the specificconstraints of high-speed trains.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present disclosure willbecome clearer from the following detailed description of some preferredembodiments thereof, made as an example and not for limiting purposeswith reference to the attached drawings. In such drawings,

FIG. 1 shows an example network, according to an embodiment of thepresent disclosure;

FIG. 2 shows an example flow of messages exchanged during a localhandoff procedure, according to an embodiment of the present disclosure;

FIG. 3 shows an example flow of messages exchanged during a globalhandoff procedure, according to an embodiment of the present disclosure;

FIG. 4 shows an example of packet forwarding through a label switchedpath (LSP) from a label-switched node to a mobile label-switched node;

FIG. 5 shows an example of packet forwarding through an LSP from amobile label-switched node to a label-switched node;

FIGS. 6-9 schematically show examples of forwarding information base(FIB) tables during operation; and

FIGS. 10-11 schematically show two disjoint LSPs and Mobile LSP Routing(MLR) functions.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

In one embodiment, a gateway label edge router receives a packetdestined for a mobile domain that comprises a vehicle label edge router.The gateway label edge router identifies, from among a plurality ofprimary domains, a particular primary domain that currently has a labelswitched connection with the mobile domain. The label switchedconnection connects the vehicle label edge router of the mobile domainand a cluster label edge router of the particular primary domain. Thegateway label edge router sends the packet to the cluster label edgerouter of the particular primary domain for transmission to the vehiclelabel edge router via the label switched connection. The gateway labeledge router tracks when the vehicle label edge router of the mobiledomain establishes a new label switched connection with a second clusterlabel edge router of a different primary domain in the plurality ofprimary domains than that of the particular primary domain.

Description

As noted above, label switched networks are networks wherein datapackets are forwarded on the basis of labels. A practical implementationof label switching could be based on Multiprotocol Label Switching(MPLS), which is an Internet Engineering Task Force (IETF) standardizedprotocol. According to MPLS, data packets entering the network at onenode, called ingress, are classified into a Forwarding Equivalence Class(FEC). All data packets with a same FEC follow a same primary path(called Label Switched Path or LSP) to a destination node, calledegress. The nodes of the network, including intermediate ones, takeper-packet forwarding decisions based on label Forwarding InformationBase (FIB) tables.

The present disclosure can be advantageously used in labelswitched-wireless mesh networks. A wireless mesh network (WMN) is acommunication network made up of nodes organized in a mesh topology. Thenodes can communicate with each other over wireless and wired links.Wireless mesh networks typically comprise mesh clients, mesh routers andoptionally gateways. The mesh clients are often laptops, surveillancecameras, industrial equipment and other network devices while the meshrouters forward traffic to and from the nodes (mesh clients and meshrouters) in the network including, if any, the gateways which may butneed not connect to the Internet. The mesh routers forward packets in amulti-hop manner to reach the intended destination within the WMN.Wireless mesh networks can be implemented with various wirelesstechnology including 802.11, 802.15, 802.16 IEEE standards, cellulartechnologies or combinations of more than one type.

Mobility management in label switched networks enables maintenance of acommunication session between a mobile node and another node of thenetwork when the mobile node moves within the network.

The widespread cellular network coverage has made ubiquitous Internetconnectivity taken for granted. Such services are evolving and arecurrently characterized by a rapid increase in their demand forbandwidth. Multimedia contents and communications, such as high-qualityvideo streaming or real time video calls, are gaining popularity andsoon end users will expect to access those services from anywhere.

At the same time, the diffusion of high-speed trains is growingworldwide as a rapid and environmentally friendly means oftransportation for long-distance mobility. Providing broadbandconnectivity on trains and subway systems to support multimedia servicesis becoming a critical service to fulfil customer expectations,appreciated in particular by business travelers.

In addition to improve customers'satisfaction, the evolution towardsIntelligent Transportation Systems (ITS) will require a new generationof services for control, automation and monitoring. The implementationof real-time video surveillance for remote surveillance of trains andthe installation of a typically of sensors and actuators for remotediagnostic and telemetry will demand for broadband connectivity that canensure reliability, customizable QoS (Quality of Service) and highbandwidth.

Wireless communication in high-speed vehicular mobility scenarios posescomplex technical challenges across several layers of the ISO-OSI stack,including the physical layer (layer 1), the data layer (layer 2) and thenetwork layer (layer 3).

Unlike a stationary environment, where roaming is rare and deferredcommunication is tolerated, in high-speed vehicular mobility scenarioshandoff is a certainty. Continuous reliable wireless connection withseamless handoff and sustained communication for smooth operation isrequired.

Moreover, as the train speed increases, communications between the trainand infrastructure encounter major difficulties of maintaining suchhigh-quality communication and yet there is no effective solution ableto cope with the specific constraints of high-speed trains. Handoff onhigh-speed trains occur more frequently and have shorter permissiblehandling times than for traditional vehicles.

High-speed mobility scenarios exhibit extreme challenges for standardnetwork layer protocols. IP address reconfiguration mechanisms, likeMobile IP, are not fast enough to react to network changes.

Handoff management is critical to provide a fluid connection and acontinuous service across the whole train path. State-of-the-arttechnologies allows handoff times in the order of a few hundredmilliseconds on the control plane and they are usually unable tomaintain a persistent connection during the process on the data plane(break-before-make approach), like in the case of the IEEE 802.11(commonly known as Wi-Fi). This level of service is insufficient toprovide an acceptable performance in high-speed mobility scenarios. Forinstance, a train traveling at 300 Km/h covers roughly 80 meters in 1second. Therefore, a handoff time of 1 second, as for the IEEE 802.11,it is insufficient to provide a good level of service. The train will betoo far away from the location where the handoff has been initiated,finding completely different channel conditions that might even preventthe handoff from successfully complete.

A key observation noted herein is that, when the network grows to a verylarge size, for example up to the order of hundreds or thousands ofnodes, the network architecture should be adapted and properlystructured in order to guarantee full scalability of the network andfacilitate the management of network reachability information. Indeed,as the network sizes grow, the traffic overhead due to the amount ofsignaling information spread over the Layer-2 network significantlyincreases.

Therefore, it is an object of the present disclosure to provide atechnique that enables to effectively manage mobility, even in networkof growing sizes (e.g. comprising hundreds or thousands of nodes).

It is a further object of the present disclosure to provide a techniquefor mobility management in a label switched network that enables toreduce signaling and information spreading through the network,bandwidth usage and employment of node resources (that is, memory usage,processing, number of FIB table entries, number of updating operationson FIB tables, and similar).

It is another object of the present disclosure to provide a techniquefor mobility management in a label switched network which is able toreact very quickly (e.g. with latency in the order of few milliseconds)to changes of the network topology due to nodes mobility, and topossibly eliminate (or significantly reduce) any loss of data packetsduring the process of mobility management and reconfiguration of thenetwork.

In some embodiments, the present disclosure relates to a method ofmobility management in a communication network comprising:

-   -   a core network comprising a Gateway Label Edge Router (G-LER);    -   an infrastructure network comprising P primary domains (C1, C2,        C3), with P≥1, each primary domain (Cj), with j integer between        1 and P, comprising Nj label switched nodes, with N≥1; and a        Cluster Label Edge Router (Cj-LER), selected from the Nj label        switched nodes,    -   a mobile network comprising K mobile domains (V1, V2, V3), with        K≥1, each mobile domain (Vi), with i integer between 1 and K,        comprising Mi label switched nodes, with Mi≥1, and a Vehicle        Label Edge Router (Vi-LER), selected from the Mi label switched        nodes,        wherein:    -   the Nj label switched nodes of the P primary domains (C1, C2,        C3) and the Mi label switched nodes of the K mobile domains (V1,        V2, V3) wirelessly communicate to each other,    -   each mobile domain (Vi) is movable with respect to the P primary        domains (C1, C2, C3), and, depending on its position with        respect to the P primary domains (C1, C2, C3), establishes a        label switched connection with one primary domain (Cj) of the P        primary domains (C1, C2, C3) at a time, via a label switched        path between the Cluster Label Edge Router (Cj-LER) of said one        primary domain (Cj) and the Vehicle Label Edge Router (Vi-LER)        of said mobile domain (Vi),    -   the Gateway Label Edge Router (G-LER) stores in a database        information about label switched paths connecting the Gateway        Label Edge Router (G-LER) with each of the Cluster Label Edge        Router (Cj-LER) of the P primary domains (C1, C2, C3);    -   for each mobile domain (Vi), the Gateway Label Edge Router        (G-LER) keeps track in said database of the primary domain (Cj)        which currently has an established label switched connection        with the mobile domain (Vi);    -   for each packet addressed to a mobile domain (Vi) of the K        mobile domains (V1, V2, V3), the Gateway Label Edge Router        (G-LER) retrieves, from said database, the primary domain (Cj)        which currently has an established label switched connection        with the mobile domain (Vi); and the packet is made to travel        along the label switched path connecting the Gateway Label Edge        Router (G-LER) to the Cluster Label Edge Router (Cj-LER) of the        primary domain (Cj) which currently has an established label        switched connection with the mobile domain (Vi), and along the        label switched path between the Cluster Label Edge Router        (Cj-LER) of the primary domain (Cj) which currently has an        established label switched connection with the mobile domain        (Vi) and the Vehicle Label Edge Router (Vi-LER) of said mobile        domain (Vi);    -   for each packet from a mobile domain (Vi) of the K mobile        domains (V1, V2, V3) to the core network, the packet is made to        travel along the label switched path between the Vehicle Label        Edge Router (Vi-LER) of said mobile domain (Vi) and the Cluster        Label Edge Router (Cj-LER) of the primary domain (Cj) which        currently has an established label switched connection with said        mobile domain (Vi), and along the label switched path connecting        the Cluster Label Edge Router (Cj-LER) of the primary domain        (Cj) which currently has an established label switched        connection with said mobile domain (Vi) and the Gateway Label        Edge Router (G-LER).

In addition, in further embodiments, the present disclosure relates to acommunication network comprising:

-   -   a core network comprising a Gateway Label Edge Router (G-LER);    -   an infrastructure network comprising P primary domains (C1, C2,        C3), with P≥1, each primary domain (Cj), with j between 1 and P,        comprising Nj label switched nodes, with Nj≥1; and a Cluster        Label Edge Router (Cj-LER), selected from the Nj label switched        nodes,    -   a mobile network comprising K mobile domains (V1, V2, V3), with        K≥1, each mobile domain (Vi), with i between 1 and K, comprising        Mi label switched nodes, with Mi≥1 and a Vehicle Label Edge        Router (Vi-LER), selected from the Mi label switched nodes,    -   wherein the Gateway Label Edge Router (G-LER), the Cluster Label        Edge Router (Cj-LER) of each primary domain (Cj) and the Vehicle        Label Edge Router (Vi-LER) of each mobile domain (Vi) are        configured so as to carry out the method according to the        present disclosure.

Preferably, all the Nj label switched nodes of the P primary domains(C1, C2, C3) and all the Mi label switched nodes of the K mobile domains(V1, V2, V3) are also configured so as to carry out the method accordingto the present disclosure.

According to another aspect, the present disclosure relates to a GatewayLabel Edge Router (G-LER) configured so as to carry out those steps ofthe method according to the present disclosure that relate to theGateway Label Edge Router (G-LER).

According to another aspect, the present disclosure relates to a ClusterLabel Edge Router (Cj-LER) of a primary domain (Cj) configured so as tocarry out those steps of the method according to the present disclosurethat relate to the Cluster Label Edge Router (Cj-LER).

According to another aspect, the present disclosure relates to a VehicleLabel Edge Router (Vi-LER) of a mobile domain (Vi) configured so as tocarry out those steps of the method according to the present disclosurethat relate to the Vehicle Label Edge Router (Vi-LER).

According to the present disclosure, the communication network is moreefficiently organized in a number of smaller broadcast domains whereeach broadcast domain is assigned an individual IP subnet. Generalcommunications between the different broadcast domains can be carriedout by standard IP routing.

The communication network is provided with a plurality of primarydomains and mobile domains, each forming a respective broadcast domain,assigned to a respective IP subnet. All packets directed to and from amobile domain are handled by means of a central unit (G-LER) in the corenetwork configured to keep track, for each mobile domain Vi, of theprimary domain which currently has an established wireless connectionwith the mobile domain as well as by means of suitable units (Cj-LER andVi-LER) in the primary domains and mobile domains, which act asingress/egress nodes of LSPs. Packets directed to and from a mobiledomain are made to travel along two disjoint Layer-2 LSPs, namely on aLSP established between a Vi-LER of the mobile domain and the Cj-LER ofthe currently connected primary domain, and a LSP established betweenthe Cj-LER of the currently connected primary domain and the G-LER inthe core network.

Mobility of the communication network is fully managed by using twolevels of Layer-2 connections (LSPs), notwithstanding the organizationof the network in multiple IP subnets.

Nodes and client devices of the mobile domains maintain their IP subnetand host addresses during mobility. In fact, when the mobile domainchanges its point of attachment to the fixed infrastructure, the wholeon-board network (with its IP subnet(s)) moves as single entity from theperspective of the rest of the network, and vice versa (networkmobility). In the present disclosure, when mobility occurs, the wholenetwork reconfiguration is entirely confined within the label-switchednodes using a limited amount of information exchange, effectively hidingthe effects of mobility to the rest of the network. In particular, noLayer-3 routing updates are sent outside the label-switched nodes, e.g.to the other switches/routers (that are not involved/active in carryingout the method of mobility management according to the presentdisclosure) and the client devices of both the fixed infrastructure andthe mobile domains.

In a mobility scenario, this enables to simplify the reconfiguration ofthe network, without disrupting its service, by limiting the signalingand information spreading through the network, the bandwidth usage andthe employment of node resources and, thus, to react very quickly (e.g.with latency in the order of few milliseconds) to changes of the networktopology due to mobility of entire broadcast domains with respect toeach other.

In the present description and claims, the term “node” is used toindicate a router or any other device (such as a PC, a mobile phone, aPDA and similar) configured so as to carry out the method of mobilitymanagement according to the present disclosure.

In the present description and claims, the expression “label-switchednode” is used to indicate a node configured to forward packets throughlabel switching (e.g., via MPLS).

In the present description and claims, the expression “client device” isused to indicate a device (such as PCs, laptops, video surveillancecameras, industrial equipment or similar devices) which may be connecteddirectly or indirectly to a label-switched node but which is not activein carrying out the method of mobility management according to thepresent disclosure. The mobility management is performed in a seamlessway with respect to client devices.

In the present description and claims, the expression “primary domain”indicates a pivot domain used as a reference domain for the mobility ofone or more mobile domains. The expression “primary domain” may includethe case of a primary domain which is movable itself.

In the present disclosure, a mobile domain is movable as a whole withrespect to a primary domain. This means that all devices (nodes, clientdevices, gateway . . . ) of a mobile domain move together, as a whole,as if they were a single piece, with respect to all devices (nodes,client devices, gateway . . . ) of a primary domain. A mobile domain canbe installed on a vehicle as, for example, a (ferry)boat, a train, asubway train, a bus, a car or similar vehicle. On the other side, aprimary domain can be installed on a railway line, coastwise, on a roadline and similar.

In the present description and claims, the expression “IP subnet”indicates a part of a communication network, having assigned an IPaddresses range with a common IP subnet prefix (e.g. 192.168.0.0/24),which is unique in the whole communication network (that is, not usedanywhere else in the rest of the communication network). Allnodes/devices in the same IP subnet share the same IP subnet prefix andare assigned an IP address belonging to the IP addresses rangecorresponding the IP subnet prefix. In the fixed infrastructure part ofthe network, each IP subnet is interconnected with the rest of thecommunication network via Layer-3 switches or routers by using IPaddressing/routing. Mobile IP subnets hosted on mobile domains areconnected to the infrastructure network through a wireless connection.

In the present description and claims, the expression “broadcast domain”indicates an IP subnet wherein all nodes and client devices can reacheach other in the data link layer by using Layer-2 (e.g. MAC)addressing.

The dependent claims refer to particularly advantageous embodiments ofthe present disclosure.

The present disclosure in at least one of the aforementioned aspects canbe implemented according to one or more of the following embodiments,optionally combined together.

Preferably, each mobile domain (Vi) establishes a label switchedconnection with one primary domain (Cj) of the P primary domains (C1,C2, C3) at a time, via a label switched path between the Cluster LabelEdge Router (Cj-LER) of said one primary domain (Cj) and the VehicleLabel Edge Router (Vi-LER) of said mobile domain (Vi), which provides atany given time an optimal connection quality according to apredetermined metric (e.g., in term of signal strength P) between themobile domain V1 and any of the primary domains C1, C2, C3.

Preferably, the Cluster Label Edge Router (Cj-LER) of each primarydomain (Cj) keeps track in a respective store of any mobile domain (Vi)which currently has an established label switched connection with it.

Preferably, the Vehicle Label Edge Router (Vi-LER) of each mobile domain(Vi) keeps track in a respective store of the (single) primary domain(Cj) which currently has an established label switched connection withit.

Preferably, for each packet addressed to a mobile domain (Vi) of the Kmobile domains (V1, V2, V3), the Cluster Label Edge Router (Cj-LER) ofeach primary domain (Cj) sends the packet directly to said mobile domain(Vi), if there is a currently established label switched connection withit, via the label switched path between said Cluster Label Edge Router(Cj-LER) and the Vehicle Label Edge Router (Vi-LER) of the mobile domain(Vi).

Preferably, for each packet addressed to a mobile domain (Vi) of the Kmobile domains (V1, V2, V3), the Cluster Label Edge Router (Cj-LER) ofeach primary domain (Cj) sends the packet to a default gateway (Cj-GW)of said primary domain (Cj) if there is not a currently establishedlabel switched connection with the mobile domain (Vi). In alternative,for each packet addressed to a mobile domain (Vi) of the K mobiledomains (V1, V2, V3), the Cluster Label Edge Router (Cj-LER) of eachprimary domain (Cj) sends the packet to the Gateway Label Edge Router(G-LER), if there is not a currently established label switchedconnection with the mobile domain (Vi), via the label switched pathconnecting said Cluster Label Edge Router (Cj-LER) to the Gateway LabelEdge Router (G-LER).

Preferably, for each packet addressed to the core network and comingfrom a mobile domain (Vi) of the K mobile domains (V1, V2, V3), withwhich it currently has an established label switched connection, theCluster Label Edge Router (Cj-LER) of each primary domain (Cj) sends thepacket to the Gateway Label Edge Router (G-LER), via the label switchedpath connecting said Cluster Label Edge Router (Cj-LER) to the GatewayLabel Edge Router (G-LER).

Preferably, the Vehicle Label Edge Router (Vi-LER) of each mobile domain(Vi) sends packets to the primary domain (Cj) which currently has anestablished label switched connection with the mobile domain (Vi), viathe label switched path between said Vehicle Label Edge Router (Vi-LER)and the Cluster Label Edge Router (Cj-LER) of said primary domain (Cj).

Preferably, before sending any packet through any of the label switchedpaths connecting the Gateway Label Edge Router (G-LER) with each of theCluster Label Edge Router (Cj-LER) of the P primary domains (C1, C2,C3), the packet is encapsulated into a Layer 2-over-Layer 3 tunnel.

Preferably, when a mobile domain (Vi) of the K mobile domains (V1, V2),having an established label switched connection with a current primarydomain of the P primary domains (C1, C2, C3), establishes a labelswitched connection with a new primary domain (Cj) of the P primarydomains (C1, C2, C3), a global handoff procedure is executed between theCluster Label Edge Router (Cj-LER) of the new primary domain (Cj) andthe Gateway Label Edge Router (G-LER).

Preferably, the label switched connection with the new primary domain(Cj) is established to provide at any given time an optimal connectionquality according to a predetermined metric (e.g., in term of signalstrength P) between the mobile domain V1 and any of the primary domainsC1, C2, C3.

Preferably, in the global handoff procedure, the Cluster Label EdgeRouter (Cj-LER) of the new primary domain (Cj) updates the respectivestore to keep track of the mobile domain (Vi) which currently has anestablished label switched connection with it.

Preferably, in the global handoff procedure, the Cluster Label EdgeRouter (Cj-LER) of the new primary domain (Cj) sends a ROUTEUPD messageto the Gateway Label Edge Router (G-LER), including information thatenables the Gateway Label Edge Router (G-LER) to keep track in saiddatabase of the new primary domain (Cj) which currently has anestablished label switched connection with the mobile domain (Vi).

Preferably, said ROUTEUPD message is sent through the label switchedpath connecting the Cluster Label Edge Router (Cj-LER) of the newprimary domain (Cj) and the Gateway Label Edge Router (G-LER).

Preferably, upon reception of the ROUTEUPD message, the Gateway LabelEdge Router (G-LER) uses the information received to update itsdatabase.

Preferably, upon reception of the ROUTEUPD message, the Gateway LabelEdge Router (G-LER) sends a further ROUTEUPD message to the ClusterLabel Edge Routers (Cj) of other primary domains of the P primarydomains (C1, C2, C3), other than the new primary domain (Cj), saidfurther ROUTEUPD message including information enabling the ClusterLabel Edge Routers (Cj) of said other primary domains to nullify anylabel switched connection previously established with the mobile domain(Vi).

Preferably, said further ROUTEUPD message is sent through the labelswitched path connecting the Gateway Label Edge Router (G-LER) and theCluster Label Edge Routers (Cj-LER) of said other primary domains.

Preferably, upon reception of the further ROUTEUPD message, the ClusterLabel Edge Routers (Cj-LER) of said other primary domains use theinformation received to update the respective stores.

Preferably, upon reception of the further ROUTEUPD message, the ClusterLabel Edge Routers (Cj-LER) of said other primary domains forward thesame ROUTEUPD message to the other label-switched nodes of the sameprimary domain (Cj), which also use the information received to updatethe respective stores.

Preferably, the label switched path between the Cluster Label EdgeRouter (Cj-LER) of each primary domain (Cj) and the Vehicle Label EdgeRouter (Vi-LER) of each mobile domain (Vi) passes through a couple of aprimary border node (SB; SB′), selected from the Nj label-switched nodesof the primary domain (Cj), and a mobile border node (MB; MB′), selectedfrom the Mi mobile label-switched nodes of the mobile domain (Vi).

Preferably, the primary border node (SB; SB′) and the mobile border node(MB; MB′) are selected as a couple of nodes, which provides at any giventime an optimal connection quality according to a predetermined metric(e.g., in term of signal strength P).

Preferably, when a current couple of primary border node (SB) and mobileborder node (MB) changes into a new couple of primary border node (SB′)and mobile border node (MB′), a local handoff procedure is executed toestablish a new label switched path between the Cluster Label EdgeRouter (Cj-LER) of the respective primary domain (Cj) and the VehicleLabel Edge Router (Vi-LER) of the respective mobile domain (Vi), saidnew label switched path passing through the new couple of primary bordernode (SB′) and mobile border node (MB′).

Preferably, in the local handoff procedure, the new mobile border node(MB′) sends a request message to the new primary border node (SB′), therequest message comprising labels adapted to enable the new primaryborder node (SB′) to form label switched paths from the new primaryborder node (SB′) to the Mi label switched nodes of the mobile domain(Vi), via the mobile border node (MB; MB′).

Preferably, at the receipt of said request message, the new primaryborder node (SB′) sends a response message to the new mobile border node(MB′), the response message comprising labels adapted to enable the newmobile border node (MB′) to form label switched paths from the newmobile border node (MB; MB′) to the Nj label switched nodes of theprimary domain (Cj), via the new primary border node (SB′).

Preferably, at the receipt of said request message, the new primaryborder node (SB′) also sends a notify message comprising stackinglabels, allocated to the Mi label switched nodes, to at least part ofthe Nj label switched nodes of the primary domain (Cj).

Preferably, at the receipt of said response message, the new mobileborder node (MB′) sends a notify message comprising stacking labels,allocated to said Nj label switched nodes of the primary domain (Cj), toat least part of the Mi label switched nodes.

Preferably, each mobile domain (Vi) is assigned to an IP subnet.

Preferably, each mobile domain (Vi) forms a broadcast domain.

Preferably, each primary domain (Cj) is assigned to an IP subnet.

Preferably, each primary domain (Cj) forms a broadcast domain.

Preferably, the core network is assigned to an IP subnet.

Preferably, the core network forms a broadcast domain.

Preferably, the core network comprises a server having said database.

Preferably, the core network comprises a default core gateway (core-GW).

Preferably, the default core gateway (core-GW) in the core networkroutes all packets addressed to a mobile domain (Vi) of the K mobiledomains (V1, V2, V3) to the Gateway Label Edge Router (G-LER).

Preferably, each primary domain (Cj) comprises a default gateway (Cj-GW)

Preferably, the default gateway (Cj-GW) of each primary domain (Cj)routes all packets to the default core gateway (core-GW). As analternative, the default gateway (Cj-GW) of each primary domain (Cj)routes all packets addressed to any mobile domain (Vi) of the K mobiledomains (V1, V2, V3) to the Cluster Label Edge Router (Cj-LER) of theprimary domain (Cj). In this latter alternative, packets other thanpackets addressed to any mobile domain (Vi) are sent to the default coregateway (core-GW).

Preferably, the label switched paths are MPLS LSPs.

Preferably, the label switched paths are Layer-2 LSPs.

Preferably, for each mobile domain (Vi), the Gateway Label Edge Router(G-LER) keeps track in said database of the primary domain (Cj) whichcurrently has an established label switched connection with the mobiledomain (Vi) by means of suitable FIB tables.

Preferably, the Cluster Label Edge Router (Cj-LER) of each primarydomain (Cj) keeps track in the respective store of any mobile domain(Vi) which currently has an established label switched connection withit by means of suitable FIB tables.

Preferably, the Vehicle Label Edge Router (Vi-LER) of each mobile domain(Vi) keeps track in the respective store of any primary domain (Cj)which currently has an established label switched connection with it bymeans of suitable FIB tables.

Preferably, the Nj label switched nodes of the P primary domains (C1,C2, C3) and the Mi label switched nodes of the K mobile domains (V1, V2,V3) wirelessly communicate to each other through at least one wirelesschannel (Fv).

FIG. 1 shows a network 1 according to an embodiment of the presentdisclosure comprising a core network 10, an infrastructure network 100and a mobile network 200. From a networking perspective, the wholenetwork 1 is organized as multiple Layer-3 (e.g. IP or Internetprotocol) subnets interconnected via Layer-3 switches or routers.

Each Layer-3 subnet is assigned an IP addresses range with a common IPsubnet prefix (e.g. 192.168.0.0/24; 192.168.10.0/24; 192.168.20.0/24;192.168.50.30/24), which is unique in the whole network 1 (not usedanywhere else in the rest of the network 1). All nodes/devices in thesame Layer-3 subnet share the same IP subnet prefix and are assigned anIP address belonging to the IP addresses range corresponding the IPsubnet prefix. Moreover, each IP subnet contains a default gateway thatinterconnects with the rest of the network through standard IP routing.On the other side, each Layer-3 subnet forms a broadcast (Layer-2)domain, meaning that within each IP subnet all nodes and devices canreach each other in the data link layer (layer 2).

The core network 10 typically contains data servers, traffic managementequipment and other critical systems. In most cases, devices locatedhere represent one end-point of nearly all communications to mobilenetwork 200. Any firewalls/gateways that provide public Internetconnectivity to clients on mobile network 200 are also hosted in thecore network 10. For the sake of simplicity, in FIG. 1 only anexemplarily data server 11 is shown, together with a Gateway Label EdgeRouter (hereinafter also shorten with the abbreviation “G-LER”) and adefault core gateway (hereinafter also shorten with the abbreviation“core-GW”).

As better explained hereinafter, the G-LER acts as ingress/egress nodeof LSPs established to manage all packets exchanged between the corenetwork 10 and mobile domains Vi.

From a networking perspective, the core network 10 is an IP subnetserved by the core-GW and having assigned an IP addresses range (e.g.192.168.0.0/24).

The wireless infrastructure network 100 comprises a (typically large)number (for example up to the order of hundreds or thousands) oflabel-switched wireless nodes that are used to provide persistentconnectivity to the mobile network 200. The label-switched wirelessnodes are connected to an existing high-speed wired backbone 400 thatprovides connectivity to several client devices deployed along thewireless infrastructure network 100 (cameras, intelligent displays,etc.).

Routing configuration and management in the backbone 400 can beimplemented either statically or dynamically using any suitable networkprotocol and it is outside the scope of this disclosure. Furthermore,the backbone 400 may contain heterogeneous segments implemented usingany suitable communication technology. Examples of such technologiesare: Ethernet, optical fiber, Layer-2 VPNs (Virtual Private Networks)over broadband xDSL (Digital Subscriber Line), wireless technologiessuch as IEEE 802.11, cellular, and similar.

According to the present disclosure and as shown in the example of FIG.1, for management and scalability reasons, the label-switched wirelessnodes in the wireless infrastructure network 100 are clustered in Pprimary domains, with P integer greater or equal than 1.

In the example of FIG. 1, three primary domains C1, C2, C3 areexemplarily shown (P=3).

Each primary domain Cj (with 1≤j≤P) comprises a number Nj of labelswitched nodes, with Nj≥1. In the example of FIG. 1, C1 has three (N1=3)label switched nodes S11, S12, S13; C2 has two (N2=2) label switchednodes S21, S22 and C3 has two (N3=2) label switched nodes S31, S32.

Moreover, each primary domain Cj comprises a number of client devices tobe managed. In the example of FIG. 1, C1 has two client devices D11,D12; C2 has two client devices D21, D22 and C3 has two client devicesD31, D32.

Each primary domain Cj is an IP (Internet protocol, Layer-3) subnet andan independent broadcast (Layer-2) domain.

As said before, this means that each primary domain Cj is assigned a IPaddresses range with a common IP subnet prefix Cj-IP (e.g.192.168.10.0/24; 192.168.20.0/24; 192.168.50.0/24), which is unique inthe whole network 1 (not used anywhere else in the rest of the network1). All label switched nodes and client devices in the same primarydomain Cj share the same IP subnet prefix and are assigned an IP addressbelonging to the IP addresses range corresponding the IP subnet prefix.Moreover, as IP subnet, each primary domain Cj is interconnected withthe rest of the network (e.g. other primary domains, mobile domains,core network 10) via Layer-3 switches or routers (by using IPaddressing/routing). On the other side, as in a broadcast (Layer-2)domain, in each primary domain Cj all nodes and devices can reach eachother in the data link layer via Layer-2 (e.g. MAC) switches/routers, byusing Layer-2 addresses.

At least one default gateway is present in each primary domain Cj toallow the local nodes and devices to reach via Layer-3 connections anyother IP subnet. In the example of FIG. 1, each primary domain Cjcomprises a default gateway (hereinafter also shorten with theabbreviation “Cj-GW”).

Moreover, according to the present disclosure each primary domain Cjalso comprises a Cluster Label Edge Router (Cj-LER), elected from the Njlabel switched nodes. In the example of FIG. 1, S11, S21 and S31 are theselected ones. The election method used to select the Cj-LER is outsidethe scope of the present disclosure.

As better explained hereinafter, the Cj-LER acts as the ingress/egresspoint of LSPs established to handle all network traffic ending,originating or passing in/through the primary domain Cj, and directedto/from the mobile network 200.

Each primary domain Cj comprises a LAN (local area network) 110providing connectivity inside the primary domain Cj. Preferably, the LAN110 is implemented by using Ethernet technology. However, othertechnologies may be used as, for example, optical fiber, Layer-2 VPNsover broadband xDSL, wireless technologies such as IEEE 802.11,cellular, and similar.

The LAN 110 can be wired (as exemplarily shown in FIG. 1) and/orwireless.

In each primary domain Cj, the Nj label switched nodes can be connectedto each other either via wired (as exemplarily shown in FIG. 1) orwireless links (or any combination of them) by means of suitablewireless/wired interfaces.

In each primary domain Cj, the Nj label switched nodes have a wirelessinterface with a radio configured to communicate on a wireless channelFv. The wireless channel Fv enables them to radio communicate with themobile network 200.

The wireless communication can be implemented, for example, by usingIEEE 802.11 technology.

The mobile network 200 comprises K mobile domains, with K integer 1.

In the example of FIG. 1, two primary domains V1, V2 are shown (K=2).

Each mobile domain Vi (with 1≤i≤K) comprises a number Mi of labelswitched nodes, with Mi≥1. In the example of FIG. 1, V1 has three (M1=3)label switched nodes M11, M12, M13 and V2 has three (M2=3) labelswitched nodes M21, M22, M23.

Moreover, each mobile domain Vi comprises a number of client devices tobe managed. In the example of FIG. 1, V1 has two client devices Dm11,Dm12 and V2 has two client devices Dm21, Dm22.

Each mobile domain Vi is an IP (Internet protocol, Layer-3) subnet andan independent broadcast (Layer-2) domain.

As said before, this means that each mobile domain Vi is assigned an IPaddresses range with a common IP subnet prefix Vi-IP1 (e.g.192.168.30.0/24), which is unique in the whole network 1 (not usedanywhere else in the rest of the network 1). All label switched nodes Miand client devices Dm11, Dm12, Dm21, Dm22 in the same mobile domain Vishare the same IP subnet prefix and are assigned an IP address belongingto the IP addresses range corresponding the IP subnet prefix. Moreover,as IP subnet, each mobile domain Vi is interconnected with the rest ofthe network 1 (e.g. other mobile domains Vi, primary domains Pj, corenetwork 10) via Layer-3 switches or routers (by using IPaddressing/routing). On the other side, as in a broadcast (Layer-2)domain, in each mobile domain Vi all nodes Mi and client devices Dm11,Dm12, Dm21, Dm22 can reach each other at the data link layer (layer 2).

According to the present disclosure, each mobile domain Vi alsocomprises a Vehicle Label Edge Router (Vi-LER), elected from the Milabel switched nodes. In the example of FIG. 1, M11 and M21 are theelected ones. The election method used to select the Vi-LER is outsidethe scope of the present disclosure.

As better explained hereinafter, the elected Vi-LER acts as theingress/egress point of LSPs established to handle all network trafficdirected to/from the rest of the network 1.

One or more additional IP subnets Vi-IPx (e.g. Vi-IP2=192.168.40.0/24)may be present on the same mobile domain Vi (besides the above-mentionedIP subnet Vi-IP1 assigned to the mobile domain Vi). In this case, anon-board router Vi-GW is responsible for routing the traffic directedto/from them. When such on-board router is present, its routingconfiguration uses the Vi-LER as the default gateway. This means thatall traffic arriving at the on-board router Vi-GW, and directed to therest of the network 1, is by default directed to the Vi-LER using anetwork interface configured on the Vi-LER's subnet Vi-IP1.

In each mobile domain Vi, the Mi label switched nodes have a wirelessinterface with a radio configured to communicate on the wireless channelFv.

Each mobile domain Vi comprises a LAN (local area network) 210 providingLayer-2 connectivity inside the mobile domain 200. Preferably, the LAN210 is implemented by using Ethernet technology. However, othertechnologies may be used as, for example, optical fiber, Layer-2 VPNs,wireless technologies such as IEEE 802.11, and similar.

The LAN 210 can be wired (as exemplarily shown in FIG. 1) and/orwireless.

Each mobile domain Vi can be a vehicle as, for example, a (ferry)boat, atrain, a subway train, a bus, a car or similar vehicle.

The P primary domains C1, C2, C3 can be installed on a railway line,coastwise, on a road line and similar.

The client devices D11, D12, D21, D22, D31, D32, Dm11, Dm12, Dm21, Dm22of the primary domains C1, C2, C3 and mobile domains V1, V2 can be, forexample, video surveillance cameras, laptops, PCs, industrial equipment,or similar.

The client devices D11, D12, D21, D22, D31, D32, Dm11, Dm12, Dm21, Dm22can be connected to the respective LANs 110, 210 either directly orthrough a wireless access point (not shown). The wireless accesspoint(s) can be, for example, a wireless modem/router, a PC, a mobilephone, a laptop or a similar device providing wireless access pointfunctionality.

In an embodiment, the Nj and Mi label-switched nodes in the P primarydomains Cj and K mobile domains Vi are label-switched routers,preferably mesh routers.

Packet forwarding among the Nj and Mi label-switched nodes in the Pprimary domains C1, C2, C3 and K mobile domains V1, V2 is performedthrough label switching. Preferably, MPLS technology is used to deliverIP-encapsulated data.

As stated above, MPLS relies on label identifiers, rather than thenetwork destination (IP) address as in traditional IP routing, todetermine the sequence of nodes to be traversed to reach the end of apath. A sequence of label-switched nodes configured to deliver packetsfrom an ingress node to an egress node using label switching is denotedas a Label Switched Path (LSP) or “tunnel”. The ingress node classifiesincoming packet according to a set of Forwarding Equivalence Classes(FECs), depending on the IP destination address of the packet; when apacket matches a class, it is marked with a label associated with theparticular class and then forwarded to the next-hop node of the LSP,according to the information configured into the Forwarding InformationBase (FIB) table of the ingress node. Subsequently, each intermediatenode manipulates the label(s) stored into the packet and then forwardsthe packet to the next-hop node, according to the information configuredinto the Forwarding Information Table (FIB) of the intermediate node.The egress node finally removes the label and handles the packet usingstandard Layer-3 (e.g. IP) routing functions. As stated above, accordingto the present disclosure, the G-LER, Cj-LERs and Vi-LERs act asingress/egress nodes of LSPs established to manage all packets exchangedbetween the core network 10 and the mobile domains Vi. The Cj-LERsprimarily act as intermediaries between the G-LER and the Vi-LERs, butthey can also act as local ingress/egress points for traffic directedto/from the Vi-LERs.

At network startup, within each primary domain Cj, the Nj label-switchednodes install intra-primary-domain label-switched paths LSPs amongstthemselves to ensure full connectivity across the primary domain Cj.Intra-primary-domain labels are suitably configured into the FIBs of theNj label-switched nodes. At network startup, within each mobile domainVi, the Mi mobile label-switched nodes install intra-mobile-domainlabel-switched paths amongst themselves to ensure full connectivityacross the mobile domain 200. Intra-mobile-domain labels are suitablyconfigured into the FIBs of the Mi mobile label-switched nodes.

The MPLS signaling which constructs said-intra-primary-domain/intra-mobile-domain label-switched paths iscarried out by a suitable protocol, according to techniques known in theart.

At network startup, no predefined inter-domain label-switched paths areinstalled between the mobile domains V1, V2 and the primary domains C1,C2, C3.

According to a preferred embodiment of the present disclosure, packetsrouting between any couple of primary domain Cj and mobile domain Vi isperformed with the intermediation of a primary border node SjB, suitablyselected from the Nj label-switched nodes of the primary domain Cj andof a mobile border node MiB, suitably selected from the Mi mobilelabel-switched nodes mobile domain Vi.

When the topology of the network 1 changes for any reason, the FIB s ofthe label-switched nodes involved in the change are suitablyreconfigured in order to adapt to the new network topology.

In a mobility scenario, wherein there is a relative motion of any mobiledomain Vi with respect to the primary domains C1, C2, C3, the FIBsreconfiguration should be performed any time, for any reason, a linkbetween a current primary border node SjB and a current mobile bordernode MiB is not any more feasible and a new link between a new primaryborder node SjB′ and a new mobile border node MiB′ has to be created.

In order to guarantee full network reachability and manage networkreachability information in this mobility scenario, the presentdisclosure provides a two-level hierarchical design having a top leveland a bottom level.

The bottom level is represented by inter-domain LSPs established betweenthe Vi-LERs and Cj-LERs of the mobile domains Vi and primary domains Cj,which are dynamically connected to each other, each time, via theintermediation of a current couple of current primary border node SjBand current mobile border node MiB. An exemplary LSP is schematicallyshown in FIG. 1 by an arrow connecting C1-LER to V1-LER.

The top level is represented by inter-domain LSPs established betweenthe G-LER and the Cj-LER of each primary domains Cj. This isschematically shown in FIG. 1 by arrows connecting the G-LER to theCj-LERs. The G-LER located in the core network 10 interconnects the Pprimary domains C1, C2, C3 and acts as an aggregator for all trafficdirected to/from the mobile domains V1, V2. By means of a route updatesignaling mechanism, described in detail later on, the G-LER has fullreachability information enabling it to reach all the mobile domains V1,V2 via the proper LSPs/Cj-LER. In particular, for each mobile domain Vi,the G-LER is anytime aware of the primary domain Cj which is currentlyconnected/linked to the mobile domain Vi.

In order to be transmitted over the Layer-3 network, among different IPsubnets and possibly the public Internet, the Layer-2 LSPs establishedbetween the G-LER and the Cj-LERs should be encapsulated in suitableLayer 2-over-Layer 3 tunnels enabling Layer-2 packets to be transportedover the Layer-3 (e.g. IP) network. Said Layer 2-over-Layer 3 tunnelsmust be created prior to installing each (G-LER, Cj-LER) Layer-2 LSP atnetwork startup. Any suitable method can be used to set up and managesaid Layer 2-over-Layer 3 tunnels, and the particular technique adoptedis outside the scope of the present disclosure.

For example, a protocol according to IETF standard L2TPv3 (Layer 2Tunneling Protocol Version 3) can be adopted as Layer 2-over-Layer 3tunneling protocol, however any other suitable protocol such as GRE(Generic Routing Encapsulation) protocol can be employed.

No Layer 2-over-Layer 3 tunnels are required to install theCj-LER-Vi-LER label switched paths because end-to-end Layer-2connectivity is available between the primary and the mobile domainsthrough the wireless channel Fv.

In order to guarantee full network reachability and manage networkreachability information in the above-mentioned mobility scenario, thenetwork routing information is configured as follows.

Core Network 10

IP subnet prefix: G-IP (e.g. 192.168.0.0/24)

Default gateway Core-GW configuration includes a set of static routes tothe G-LER for all mobile domain subnets; in other words it is configuredto send all packets received by it and directed to a mobile domain Vi ofthe K mobile domains V1, V2, V3 to the G-LER.

The G-LER has FIB tables suitably configured and updated to enable theG-LER to send all packets directed to a mobile domain Vi via the primarydomain Cj, which is currently connected/linked to the mobile domain Vi.

Backbone 400

The backbone is a Layer-3 network that enables the default gatewayCore-GW of the core network 10 and the default gateway Cj-GW of theprimary domains Cj to communicate using standard IP routing.

Primary Domain Cj

IP subnet prefix: Cj-IP1 (e.g. 192.168.10.0/24).

Default gateway Cj-GW may be configured to send all traffic directed toa mobile domain Vi to Core-GW (which, in turn, has a static route to theG-LER), the Core-GW being reachable through conventional IP routing inthe backbone 400.

According to an alternative, the default gateway Cj-GW may be configuredto send all traffic directed to a mobile domain Vi to the respectiveCj-LER (which is directly connected to the G-LER via the respectiveLSP), and any other unknown destination address to Core-GW.

The Cj-LER has FIB tables suitably configured and updated to enable theCj-LER:

-   -   to send packets directed to any currently connected/linked        mobile domain Vi to the respective Vi-LER via the LSP connecting        the Cj-LER to the Vi-LER;    -   to preferably send packets directed to any label switched nodes        (other than the Vi-LER, e.g. M12, M13, M22 or M23) of the        currently connected/linked mobile domain Vi directly to said        label switched node (without passing via the respective Vi-LER)        via the LSP connecting the Cj-LER to said label switched node;    -   to send any packet directed to the G-LER via the LSP connecting        the Cj-LER to the G-LER;    -   to send—as default route—any destination address that is unknown        to its FIB tables to the G-LER via the respective LSP connecting        said Cj-LER to the G-LER.

Mobile Domain Vi

IP subnet prefix: Vi-IP1 range.

Vi-GW router is configured with a default route to the Vi-LER. Vi-GWrouter may be connected to additional LANs corresponding to Vi-IPxsubnet prefixes so that packets to said subnets are routed via anappropriate LAN interface of the Vi-GW router.

The Vi-LER has FIB tables suitably configured and updated to enable theVi-LER:

-   -   to send packets directed to any currently connected/linked        primary domain Cj to the respective Cj-LER via the LSP        connecting said Cj-LER and Vi-LER;    -   to send packets directed to any additional internal mobile        domain subnets Vi-IPx (e.g. Vi-IP2, etc) to the on-board router        Vi-GW.    -   to send—as default route—any destination addresses unknown to        his FIB tables (including those relating to any other mobile        domain or any primary domain not currently connected to it) to        the Cj-LER of the currently connected/linked primary domain Cj;    -   to preferably send packets directed to any label switched nodes        (other than the Cj-LER, e.g. S12, S13, S22, S32) of the        currently connected/linked primary domain Cj directly to said        label switched node (without passing via the respective Cj-LER)        via the LSP connecting the Vi-LER to said label switched node.

Other internal Vi-IPx subnets: devices belonging to any additionalsubnets located on the mobile domain Vi are configured with a defaultroute to Vi-GW.

In a mobility scenario, any time there is a relative motion of anymobile domain Vi with respect to the primary domains C1, C2, C3, inorder to guarantee full network reachability and manage networkreachability information, a handoff procedure is performed according tothe present disclosure, as disclosed in detail below.

The mobile label-switched nodes M11, M12, M13, M21, M22, M23 of themobile domains V1, V2, the G-LER, and the label-switched nodes S11, S12,S13, S21, S22, S31, S32, of the primary domains C1, C2, C3advantageously comprise at least one processor coupled to one or morenetwork interfaces and a memory that stores a process (e.g., softwareand/or firmware modules) that, when executed, is configured to performany or all of the techniques in the present disclosure.

Handoff Procedure

Let's assume that at a certain time mobile domain V1 is connected toprimary domain C1 via a current primary border node S1B and a currentmobile border node M1B.

Let also be S11 the C1-LER of C1 and M11 the V1-LER of V1.

The complete handoff procedure can be split in two steps: 1) a localprocedure, which is used to create updated LSPs between the mobiledomain V1 and the primary domain C1 (INTRA-CLUSTER handoff) or to createnew LSPs between the mobile domain V1 and any other primary domain C2,C3 (INTER_CLUSTER handoff); and 2) a global procedure, which is used topropagate the reachability information of mobile domain V1 to the G-LERand to all primary domains C1, C2, C3.

Local Procedure

According to an embodiment of the present disclosure, for mobile domainV1 and primary domains C1, C2, C3, current primary border node S1B andcurrent mobile border node M1B are dynamically selected among the mobilelabel-switched nodes M11, M12, M13 and the label-switched nodes S11,S12, S13, S21, S22, S31, S32 in a continuous process. The mobilelabel-switched nodes M11, M12, M13, which operate on the wirelesschannel Fv, continuously monitor the quality of the wireless signalsreceived from each node S11, S12, S13, S21, S22, S31, S32 of the primarydomains C1, C2, C3, which also operate on said wireless channel Fv.

Said mobile label-switched nodes M11, M12, M13 periodically send (e.g.every 100 ms) to a specific node, designed among M11, M12, M13 to act asa mobile domain master node M1M, a message containing the wireless linkquality statistics collected in the last time span. The master node M1Mcollects and merges the messages received from said mobilelabel-switched nodes M11, M12, M13 and, optionally, also data from itsown measurements, and it processes the aggregated data to determine acouple of nodes (M1B, SjB) which provides at any given time an optimalconnection quality according to a predetermined metric (e.g., in term ofsignal strength P or other metrics) between the mobile domain V1 and anyof the primary domains C1, C2, C3 currently within the communicationrange.

When the current couple (M1B, S1B) changes into a new couple (e.g. intoM1B′, S1B′), and the new primary border node S1B′ belongs to the sameprimary domain C1 of the current primary border node S1B, anINTRA-CLUSTER hand-off is performed and only a local handoff procedureis executed.

This means that reachability information (FIB) updates are confinedwithin the primary domain C1 and mobile domain V1 and no changes outsideC1 and V1 are required, so there is no need to execute the globalprocedure.

On the other side, when the current couple (M1B, S1B) changes into a newcouple (e.g. into M1B′, S2B′), and the new primary border node S2B′belongs to a new primary domain, e.g. C2, with respect to the currentprimary border node S1B, an INTER-CLUSTER hand-off is performed, andboth local and global handoff procedures are executed.

Indeed, in this case, reachability information (FIB) updates areextended to all primary domains C1, C2, C3 as well as to the G-LER.

In any case, when the new mobile border node M1B′ is selected, itreceives a notification message from the master node MM, recognizesitself as the newly elected mobile border node, and runs a local handoffprocedure for establishing a label switched connection with the newprimary border node (e.g. S1B′ or S2B′).

The local handoff procedure comprises three main phases: 1) a handoffrequest phase performed by the new mobile border node M1B′; 2) a handoffresponse phase performed by new the primary border node (e.g. S1B′ orS2B′); and 3) a handoff notification phase, performed independently bothby the new mobile border node M1B′ and the new the primary border node(e.g. S1B′ or S2B′).

The flow of messages exchanged during the three phases is illustratedschematically by the diagram of FIG. 2.

In the example of FIG. 2 an INTRA-CLUSTER hand-off is considered whereinthe new primary border node is S1B′ (which corresponds to S12) and M1B′corresponds to M12.

The handoff request phase comprises the transmission of a signaling REQ(request) message from the new mobile border node M1B′ to the newprimary border node S1B′. Such REQ message is preferably sent over thewireless channel Fv directly to the Layer-2 MAC address of the primaryborder node SIB′, since it is assumed that, due to service disruptioncaused by mobility, the standard IP routing layer can be unable todeliver data during the handoff transitory.

The REQ message preferably comprises the following information: M1B′MAC; MD_ID; SEQ_NUM; MDL_LIST.

MB′ MAC is the MAC address of the wireless radio interface of the mobileborder node M1B′.

MD_ID (Mobile Domain IDentifier) is a unique identifier, which can be aninteger number assigned (for example by the network administrator) tothe mobile domain V1 (it has the same value for all the mobilelabel-switched nodes M11, M12, M13 of the mobile domain V1).

SEQ_NUM is a sequence number received from the master node MM.

MDL_LIST (Mobile Domain Label List) comprises M1 (in the example M1=3)labels to be used by the primary border node S1B′ to respectivelyforward packets, via the mobile border node M1B′, to M11, M12, M13.

According to the present disclosure, the REQ message also comprises aV-LER_ID, as for example a MPLS label associated to the V1-LER of themobile domain V1, and a list MDS_LIST (Mobile Domain Subnet list) of anyFEC relating to any on-board IP subnets (e.g. V1-IP1 and V1-IP2) presentin the mobile domain, to be used by the primary border node S1B′ torespectively forward packets, via the mobile border node M1B′, to theV1-LER for FEC=FEC_V1-LER and for any FEC relating to the on-board IPsubnets (e.g. V1-IP1 and V1-IP2) present in the mobile domain V1.

When the primary border node S1B′ receives the REQ message sent by themobile border node M1B′, it performs the handoff response phase,preferably according to the following actions:

It checks the validity of the received handoff sequence number SEQ_NUMfor the particular mobile domain V1 (identified by MD_ID). If themessage is found to be old or a duplicate, it is discarded. This checkand the use of the SEQ_NUM parameter can be useful for discarding old orduplicate handoff request messages.

It sends a signaling RES (response) message to the mobile border nodeM1B′. Similarly, as above, this message is preferably sent directly tothe Layer-2 MAC address of the mobile border node M1B′ via the wirelesslink. The RES message preferably comprises the following information:SEQ_NUM (that is, the sequence number as received in the REQ message)and PDL_LIST. The PDL_LIST (Primary Domain Label List) parametercomprises N1 labels to be used by the mobile border node M1B′ torespectively forwards packets, via the primary border node S1B′, to theN1 label-switched nodes S11, S12, S13 of primary domain C1 (in theexample N1=3). Optionally, the RES message may also comprise the PD_ID(that is a unique identifier, which can be an integer number, assignedto the primary domain C1). Furthermore, according to the presentdisclosure, the RES message comprises a C1-LER_ID, as for example a MPLSlabel associated to the C1-LER of the mobile domain C1, and the FECcorresponding to the C1-IP1 subnet, to be used by the mobile border nodeM1B to respectively forwards packets, via the primary border node S1B′,to the C1-LER for any unknown address and in association withFEC=C1-IP1.

It uses the M1 labels received in the MDL_LIST and the other parametersof the REQ message for configuring/updating its FIB tables withappropriate entries. As explained in more detail below, such entriesdetermine the installation of individual LSPs from the primary bordernode S_1B′ towards the M1 mobile nodes M11, M12, M13.

Preferably, step 2) is performed before step 3) in order to avoid anydelay in sending the RES message to the mobile border node M1B′.

When the mobile border node M1B′ receives the RES message from theprimary border node S1B′, it performs the following actions:

It checks the validity of the received sequence number SEQ_NUM bymatching it with the value transmitted into the REQ message. If themessage is found to be old or a duplicate, it is discarded.

It uses the N1 labels received in the PDL_LIST and the other parametersof the RES message for configuring/updating its FIB tables withappropriate entries. As explained in more detail below, such entriesdetermine the installation of individual LSPs from the mobile bordernode M1B′ towards the N1 primary nodes S11, S12, S13.

The handoff notification phase is executed by the primary border nodeS1B′ and the mobile border node M1B′ with the purpose of distributinghandoff configuration data amongst the other label switched nodes (S11,S13, and M11, M13) in the primary domain C1 and mobile domain V1,respectively, which do not directly participate in the handoff procedurebetween S1B′ and M1B′. Preferably, the primary border node S1B′ executesthe handoff notification phase right after sending the RES message (thatis, after action 2) and before action 3) above mentioned), while themobile border node M1B′ preferably executes the handoff notificationphase right after reception of the RES message received from 1B′ (thatis, after action 1′) and before action 2′) above mentioned).

The handoff notification phase comprises the transmission of a NOTIFYmessage to the other label switched nodes. In the example of FIG. 2, theprimary border node S1B′ sends a NOTIFY message to S11 and S13, and themobile border node M1B′ sends a NOTIFY message to M11 and M13.

The NOTIFY message sent by the primary border node S1B′ advantageouslycomprises the following information: SEQ_NUM (that is, the sequencenumber as received in the REQ message) and PDSL_LIST. The PDSL_LIST(Primary Domain Stacking Label List) parameter comprises M1 stackinglabels allocated to the M1 mobile label-switched nodes, which enable thenotified label switched nodes of the primary domain C1 (in the exampleS11 and S13) to forward packets, via the primary border node S1B′ (inthe example, S12), directly to the M1 mobile label-switched nodes (inthe example, M11, M12 and M13).

Moreover, according to the present disclosure, the NOTIFY message alsocomprises the stacking label associated to the V1-LER of the mobiledomain V1, and the list MDS_LIST (Mobile Domain Subnet list) of any FECrelating to any on-board IP subnets (e.g. V1-IP1 and V1-IP2) present inthe mobile domain V1, which enable the notified label switched nodes ofthe primary domain C1 (in the example S11) to forward packets, via theprimary border node S1B′ (in the example, S12), to the V1-LER for anyFEC relating to the on-board IP subnets (e.g. V1-IP1 and V1-IP2).

The NOTIFY message sent by the mobile border node M1B′ advantageouslycomprises the following information: SEQ_NUM (that is, the sequencenumber as sent in the REQ message) and MDSL_LIST. The MDSL_LIST (MobileDomain Stacking Label List) parameter comprises N1 stacking labelsallocated to the N1 primary label-switched nodes, which enable thenotified mobile label switched nodes of the mobile domain V1 (in theexample M11 and M13) to forward packets, via the mobile border node M1B′(in the example, M12), directly to the N1 primary label-switched nodes(in the example, S11, S12 and S13.

Moreover, according to the present disclosure, said NOTIFY message alsocomprises the stacking label associated to the C1-LER of the primarydomain C1 and the FEC corresponding to the C1-IP1 subnet, which enablethe notified mobile label switched nodes of the mobile domain V1 (in theexample M11) to forward packets, via the mobile border node M1B′ (in theexample, M12) to the C1-LER for any unknown address and for the FECcorresponding to the C1-IP1 subnet.

When a label-switched node (in the example, M11, M13, S11, S13) receivesa NOTIFY message, it preferably performs the following actions:

It checks the validity of the received sequence number SEQ_NUM for thespecific mobile domain V1 identified by MOB_ID. If the message is old ora duplicate, it is discarded.

It uses the information received in the NOTIFY message forconfiguring/updating its FIB tables with appropriate entries. Asexplained in more detail below, such entries suitably determine theinstallation of individual LSPs from the N1 label-switched nodes to theM1 mobile label-switched nodes via the couple S1B′-M1B′ and, vice versa,from the M1 mobile label-switched nodes to the N1 label-switched nodesvia the couple M1B′-S_1B′. Such LSPs all include a link between S_1B′and M1B′, in both directions.

In addition, according to the present disclosure, each label switchednode S11, S12, S13 of primary domain C1 uses the label associated to theV1-LER of the mobile domain V1 to install a FEC into its FTN table tomatch any IP subnet prefix (e.g. V1-IPx) advertised in the REQ/NOTIFYmessage. In this way, all packets directed to any on-board IP subnetprefix (e.g. V1-IP1 and V1-IP2) will be forwarded to the V1-LER of themobile domain V1.

Moreover, according to the present disclosure, each mobile labelswitched node M11, M12, M13 of mobile domain V1 uses the labelassociated to the C1-LER of the primary domain C1 a) to install a FECinto its FTN table to match IP subnet prefix C1-IP1 of primary domain C1advertised in the RES/NOTIFY message, and b) to install a FEC into itsFTN table to match all unknown destination IP subnets (default route).This includes, for example, all traffic directed to a public internetaddress or to a core network subnet. In this way, all packets directedto the IP subnet prefix C1-IP1 as well as to any unknown destination IPsubnets will be forwarded to the C1-LER of the primary domain C1.

Global Procedure

This procedure is started by the Cj-LER of a primary domain Cj. TheCj-LER is able to detect that an INTER-CLUSTER handoff is occurring byexamining the advertised IP subnet prefixes when it receives a handoffNOTIFY message from a primary border node of the primary domain Cj or adirect handoff REQ message from a mobile border node of mobile domainVi. If the advertised IP subnet prefixes are not found by the Cj-LER inits FTN table, it means that the mobile domain Vi was previouslyconnected to a different, previous primary domain Cj. In this case, theCj-LER executes the global handoff procedure to notify the G-LER thatthe mobile domain Vi is now reachable via such new Cj-LER. On the otherhand, if the advertised IP subnet prefixes are found in the FTN table ofthe Cj-LER, it means that the mobile domain Vi was already connected toprimary domain Cj. In this case, only the local handoff procedure isexecuted.

The messages exchanged to execute the global procedure are schematicallyillustrated in FIG. 3.

In the example of FIG. 3, the global procedure is started by the C1-LERof primary domain C1 when it receives a handoff NOTIFY message from aprimary border node of the primary domain C1 or a direct handoff REQmessage from a mobile border node of mobile domain Vi.

The C1-LER sends a ROUTEUPD message to the G-LER. The ROUTEUPD messageincludes an association between the IP subnet prefix (e.g. V1-IP1 andV1-IP2) of any on-board IP subnets advertised by the mobile domain V1and the C1-LER's ID (e.g. MPLS label). This message is sent through theLSP installed between the C1-LER and the G-LER over the Layer2-over-Layer 3 tunnel.

Upon reception of the ROUTEUPD message, the G-LER uses the C1-LER's IDto update a FEC into its FTN tables to match the IP subnet prefix (e.g.V1-IP1 and V1-IP2) advertised in the ROUTEUPD message.

Subsequently, the G-LER sends another ROUTEUPD message to the C2-LER andC3-LER of the other primary domains C2 and C3 as shown in FIG. 3. Also,this ROUTEUPD message includes the IP subnet prefix (e.g. V1-IP1 andV1-IP2) of any on-board IP subnets advertised by the mobile domain V1.However, in this case the associated Cj-LER ID is NULL, so that therecipients will delete all FIB entries (particularly in the FTN)relating to mobile domain V1. Consequently, any traffic originating fromthe local subnet of primary domains C2 and C3 or from alocally-connected mobile domain (different from V1, e.g. V2) anddirected to mobile domain V1 will be sent to the G-LER, which acts asthe default gateway for all mobile primary domains V1, V2.

To ensure consistency across the whole network, the C2-LER and C3-LERforward the same ROUTEUPD message to the other label-switched nodes(e.g. S21 and S32) of the same primary domain C2 and C3, which apply thesame changes to their FIBs.

Concerning the packets to be sent between a mobile domain Vi and aprimary domain Cj through LSPs, it is noted that said packets aremarked, for part of the LSP, using two stacked labels by means of labelstacking.

In particular, as schematically shown in FIG. 4, a packet to be sentthrough an LSP from a given label-switched node (e.g. S11) to a givenmobile label-switched node (e.g. M11) is advantageously marked with aninner label (e.g. LS12M11B) and an outer label (e.g. LS11S12). The outerlabel will correspond to the intra-primary-domain label to be used byS11 to forward packets to S1B′ (e.g. S12) via an intra-primary-domainLSP in the primary domain C1. The inner label will correspond to thestacking label, received by S11 in the NOTIFY message, enabling S11 toforward packets to M11 via the link S1B′-M1B′. When, through theintra-primary-domain LSP, the packet reaches S1B′, the latter pops (thatis, remove) the outer label (e.g. LS11S12) and swaps the inner label(e.g. LS12M11B) with the label (e.g. LM12M11B) of the labels received inthe REQ message that enables S1B′ to forward the packet to M11 via M1B′.When M1B′ receives the packet, it swaps the current label (e.g.LM12M11B) with the intra-mobile-domain label (e.g. LM12M11) enablingM1B′ to forward packets to M11 through an intra-mobile-domain LSP in themobile domain V1.

Similarly (as schematically shown in FIG. 5), a packet to be sentthrough a LSP from a given mobile label-switched node (e.g. M11) to agiven primary label-switched node (e.g. S11) is advantageously markedwith an inner label (e.g. LM12S11B) and an outer label (e.g. LM11M12).The outer label will correspond to the intra-mobile-domain labelenabling M11 to forward packets to M1B′ (e.g. M12) via anintra-mobile-domain LSP within the mobile domain V1. The inner labelwill correspond to the stacking label, as received by M11 in the NOTIFYmessage, to be used by M11 to forward packets to S11 via the linkM1B′-S1B′. When, through the intra-mobile-domain LSP, the packet reachesM1B′, the latter pops the outer label (e.g. LM11M12) and swaps the innerlabel (e.g. LM12S11B) with the label (e.g. LS12S11B) of the labelsreceived in the RES message that enables M1B′ to forward the packet toS11 via S1B′. When S1B′ receives the packet, it swaps the current label(e.g. LS12S11B) with the intra-primary-domain label (e.g. LS12S11)enabling S1B′ to forward packets to S11 through an intra-primary-domainLSP in the primary domain C1.

FIGS. 6 to 9 schematically show examples of FIB tables in the case of aprimary domain C1 comprising two label-switched nodes S11 and S12 and ofa mobile domain V1 comprising two label-switched nodes M1 and M2.

In each of S11, S12, M1, M2 the FIB tables comprise an FTN (FEC toNHLFE) table, an ILM (Incoming Label Mapping) table and a NHLFE (NextHop Label Forwarding Entry) table.

The FTN tables provide correspondences between predetermined FECs andpredetermined indexes (NHLFE in) to be used as access keys to the NHLFEtable.

The ILM tables provide correspondences between predetermined inputlabels (LABEL IN) and predetermined indexes (NHLFE in) to be used asaccess key to the NHLFE table.

In correspondence of each index (NHLFE in), the NHLFE tables provideinformation about operation to be performed on input label (Label OP),about the output label to be used (Label OUT) and about the next-hopnode for packet forwarding (Next).

FIG. 6 represents a situation wherein at a certain time mobile domain V1is connected to primary domain C1 via S12 as current primary border nodeS1B and M2 as current mobile border node M1B. It is also assumed thatS11 is the C1-LER of C1 and M11 is the V1-LER of V1. Let also be node G1(mentioned in the tables and shown in FIGS. 7-8) the G-LER of the corenetwork 10, C1_IP1 the subnet prefix of the subnet of C1, and V1_IP1 andV1_IP2 the IP subnet prefixes of on-board subnets of V1.

In this example of FIG. 6, intra-primary-domain LSPs are pre-installedwithin the primary domain C1 (between S11 and S12) andintra-mobile-domain LSPs are pre-installed within the mobile domain Vi(between M1 and M2). Moreover, following to a local handoff procedurebetween S12 and M2, LSPs are installed between the primary domain C1 andthe mobile domain V1 via the primary/mobile border nodes S12 and M2.

As shown in FIG. 6, during the local handoff procedure:

The REQ message from M2 to S12 comprises: a label LM2OUT in associationwith FEC=F_M2, a label LM2M1B in association with FEC=FEC_M1 and withV1-LER; and the MDS_LIST (Mobile Domain Subnet list) of any FEC relatingto any on-board IP subnets (e.g. V1-IP1 and V1-IP2) of V1.

The RES message from S12 to M2 comprises: label LS12OUT in associationwith FEC=F_S12, label LS12S11B in association with FEC=FEC_S11 and withC1-LER; and the FEC corresponding to the C1-IP1 subnet.

The NOTIFY message from S12 to S11 comprises: stacking label LS12M1B inassociation with FEC=F_M1 and with V1-LER, stacking label LS12M2B inassociation with FEC=F_M2, and the MDS_LIST (Mobile Domain Subnet list)of any FEC relating to any on-board IP subnets (e.g. V1-IP1 and V1-IP2)of V1.

The NOTIFY message from M2 to M1 comprises: stacking label LM2S11B inassociation with FEC=F_S11 and C1-LER; stacking label LM2S12B inassociation with FEC=F_S12, and the FEC corresponding to the C1-IP1subnet.

During the local handoff procedure, the FIB tables on S11, S12, M1, M2are adjusted with updated entries, adapted to install the new LSPsbetween the primary domain C1 and the mobile domain V1 via theprimary/mobile border nodes S12 and M2. The results of such adjustmentsare shown in the tables of FIG. 6.

According to the table FTN of S11 (FTN(S11)):

At the receipt of a packet with FEC=F_S12, S11 will access the NHLFEtable with the index I1, will PUSH (that is assign) label LS11S12 to thepacket and will send it to node S12.

At the receipt of a packet with FEC=F_G1, S11 will access the NHLFEtable with the index IG, will PUSH (that is assign) label LS11G1 to thepacket and will send it to node G1 (G-LER).

At the receipt of a packet with FEC=M1, S11 will access the NHLFE tablewith the index I2, will PUSH (that is assign) the (inner) label LS12M1Bto the packet, will access the NHLFE table again with the index I1, willPUSH (that is assign) the (outer) label LS11S12 to the packet, and willsend the packet to node S12.

At the receipt of a packet with FEC=F_M2, S1 will access the NHLFE tablewith the index 13, will PUSH (that is assign) the (inner) label LS12M2Bto the packet, will access the NHLFE table again with the index I1, willPUSH (that is assign) the (outer) label LS11S12 to the packet, and willsend the packet to node S12.

At the receipt of a packet with FEC=V1_IP1, S1 will access the NHLFEtable with the index 12, will PUSH (that is assign) the (inner) labelLS12M1B to the packet, will access the NHLFE table again with the indexI1, will PUSH (that is assign) the (outer) label LS11S12 to the packet,and will send the packet to node S12.

At the receipt of a packet with FEC=V1_IP2, S1 will access the NHLFEtable with the index 12, will PUSH (that is assign) the (inner) labelLS12M1B to the packet, will access the NHLFE table again with the indexI1, will PUSH (that is assign) the (outer) label LS11S12 to the packet,and will send the packet to node S12.

At the receipt of a packet with FEC=default, S1 will access the NHLFEtable with the index IG, will PUSH (that is assign) label LS11G1 to thepacket and will send it to node G1 (G-LER).

According to the table ILM of S1 (ILM(S11)):

At the receipt of a packet with input label LS11OUT, S11 will access theNHLFE table with the index I0 and will POP (that is remove) labelLS11OUT from the packet and will pass the packet to upper layers of thenetwork.

At the receipt of a packet with input label LS12S11, S1 will access theNHLFE table with the index I0 and will POP label LS12S11 from the packetand will pass the packet to upper layers of the network.

At the receipt of a packet with input label LS11S12B, S1 will access theNHLFE table with the index I1B, will SWAP (that is change) the labelLS11S12B into LS11S12 and will send the packet to node S12.

At the receipt of a packet with input label LG1S11, S11 will access theNHLFE table with the index I0, will POP label LG1S11 from the packet andwill send it to the upper layer of the network.

At the receipt of a packet with input label LS11M1B, S11 will access theNHLFE table with the index I2B, will SWAP (that is change) the labelinto LS12M1B, will access the NHLFE table again with the index I1, willPUSH (that is assign) the (outer) label LS11S12 to the packet, and willsend the packet to node S12.

At the receipt of a packet with input label LS11M2B, S11 will access theNHLFE table with the index I3B, will SWAP (that is change) the labelinto LS12M2B, will access the NHLFE table again with the index I1, willPUSH (that is assign) the (outer) label LS11S12 to the packet, and willsend the packet to node S12.

Similar observations apply to the tables of S12, M1, M2.

In general, it is noted that the FEC=default is used to indicate allunknown IP prefixes, not present in the respective FTN. It is also notedthat FEC=default is not present in the FTN table of S12 because allunknown IP prefixes, not present in the FTN of this node are forwardedto the C1-GW. Indeed, for the purpose of managing the traffic betweenthe mobile domain V1 and the rest of the network 1, S12 is only anintermediary node (between the C1-LER S11 and the mobile domain V1), andits default route needs not to be consulted to forward such traffic.

FIG. 7 represents the same situation of FIG. 6, wherein the G-LER (G1)and primary domain C2 are also shown. Regarding primary domain C2, itassumed that it comprises two label-switched nodes S21 and S22 and thatS21 is the C2-LER of C2. Two LSPs are installed respectively between theG-LER and the C1-LER and between the G-LER and the C2-LER, over theLayer 2-over-Layer 3 tunnels.

In the situation of FIG. 7, it is assumed that a global handoffprocedure was executed by C1-LER to notify the G-LER that the mobiledomain V1 is connected to primary domain C1 via the C1-LER, and thatROUTEUPD messages were exchanged.

In particular, as shown in FIG. 7, during the global handoff procedure:

In the ROUTEUPD message from S11 to G1, the ID of S11 is sent as LER IDin association with FEC=V1_IP1 and FEC=V1_IP2. The ID of S11 may be aMPLS label (e.g. LG1S11) or the IP address of S11.

In the ROUTEUPD message from G1 to S21, a NULL value is sent as LER IDin association with FEC=V1_IP1 and FEC=V1_IP2.

In the ROUTEUPD message from S21 to S22, a NULL value is sent as LER IDin association with FEC=V1_IP1 and FEC=V1_IP2.

During the global handoff procedure, the FIB tables on G1, S11, S12,S21, S22 are changed with updated entries that enable the G-LER to reachthe mobile domain V1 via the primary domain C1. The results of suchadjustments are shown in the tables of FIG. 7.

According to the table FTN of G1 (FTN(G1)):

At the receipt of a packet with FEC=F_S11, G1 will access the NHLFEtable with the index I1, will PUSH (that is assign) label LG1S11 to thepacket and will send it to node S11 via the established LSP over theL2TP tunnel.

At the receipt of a packet with FEC=F_S21, G1 will access the NHLFEtable with the index I2, will PUSH (that is assign) label LG1S21 to thepacket and will send it to node S21 via the established LSP over theL2TP tunnel.

At the receipt of a packet with FEC=V1_IP1 or FEC=V1_IP2, G1 will accessthe NHLFE table with the index I1, will PUSH (that is assign) labelLG1S11 to the packet and will send it to node S11 via the establishedLSP over the L2TP tunnel. In this way, all packets directed to mobiledomain V1 (that is, all packets having an IP address belonging to the IPsubnet prefix V1_IP1 or V1_IP2) are sent by the G-LER to the C1-LER(S11).

According to the table ILM of G1 (ILM(G1)):

At the receipt of a packet with input label LG1OUT, LS11G1 or LS21G1, G1will access the NHLFE table with the index I0 and will POP (that isremove) said input label from the packet and will pass the packet toupper layers of the network.

Similar observations apply to the tables of S1 and S21.

It can be noted that—as primary domain C2 is no connected to any mobiledomain Vi—the tables of S21 (and S22) have no entries relating to mobiledomains V1 or any other mobile domain.

FIG. 8 represents a development of the situation of FIG. 7 wherein aglobal handoff procedure is executed for connecting the mobile domain V1via the primary domain C2 (instead of the primary domain C1), whereinS22 and M2 respectively act as new primary border node S2B′ and mobileborder node M2B′.

In particular, in the situation of FIG. 8, it is assumed that a globalhandoff procedure has been executed by C2-LER (S21) to notify the G-LERthat the mobile domain V1 is now connected to primary domain C2 via theC2-LER, and ROUTEUPD messages were exchanged according to the presentdisclosure.

In particular, as shown in FIG. 8, during said global handoff procedure:

In the ROUTEUPD message from S21 to G1, the ID of S21 is sent as LER IDin association with FEC=V1_IP1 and FEC=V1_IP2. The ID of S21 may be aMPLS label (e.g. LG1S21) or the IP address of S21.

In the ROUTEUPD message from G1 to S11, a NULL value is sent as LER IDin association with FEC=V1 IP1 and FEC=V1 IP2.

In the ROUTEUPD message from S11 to S12, a NULL value is sent as LER IDin association with FEC=V1 IP1 and FEC=V1 IP2.

Accordingly, the FIB tables on G1, S11, S12, S21, S22 are updated withentries adapted to enable the G-LER to reach the mobile domain V1 viathe primary domain C2.

In particular, with respect to the situation of FIG. 7, it can be notedthat—as primary domain C1 is no connected anymore to mobile domainV1—the tables of S11 (and S12) have no more entries relating to mobiledomains V1. On the other side, entries relating to mobile domains V1have been added into the tables of S21 (and S22).

FIG. 9 represents the whole FIB tables of nodes S21, S22, M1, M2 in thesituation of FIG. 8, after (besides the global handoff procedure) alocal handoff procedure has been executed to connect the mobile domainV1 to the primary domain C2, via the intermediation of M2 and S22 as newprimary border node S2B′ and mobile border node M2B′.

The tables entries and the REQ, RES, NOTIFY messages exchanged duringthe local handoff procedures are similar to those already explained withreference to FIG. 6, to which reference is made.

According to the present disclosure, compared to standard MPLS dataplane functions, G-LER, Cj-LER and Vi-LER units perform an additionaltask to send packets via two disjoint LSPs (one LSP from G-LER andCj-LER and one LSP from Cj-LER and Vi-LER). This additional task isperformed in the G-LER, Cj-LER and Vi-LER by a Mobile LSP Routing (MLR)function, as schematically shown in FIGS. 10 and 11.

More specifically, in each Cj-LER the MLR is responsible for determiningwhether the packet reaching the Cj-LER from the Vi-LER or the G-LERshould be respectively transmitted to the G-LER or the Vi-LER viaanother LSP, or to the internal LAN 110.

With reference to FIGS. 1, 7 and 10, let's consider a packet received bythe G-LER from the core network 10 (via core-GW) and directed to aclient device Dm11 connected to the on-board LAN 210 of mobile domainV1, having destination IP address belonging to the V1-IP1 range (e.g.192.168.30.0/24). V1 is connected to primary domain C1, which is managedby the C1-LER S11, as in the situation shown of FIG. 7.

According to the tables shown in FIG. 7, the G-LER (G1) accesses the FECtable with FEC=V1_IP1 so that it will access the NHLFE table with theindex I1, will PUSH (that is assign) label LG1S11 to the packet and willsend it to node S11 (C1-LER) via the established LSP1 over the Layer2-over-Layer 3 tunnel.

On the C1-LER the packet is decapsulated from the Layer 2-over-Layer 3tunnel and then it is processed by the MLR. The MLR accesses the FECtable with FEC=V1_IP1. As such FEC=V1_IP1 is present in its FEC table,it finds out that the IP destination address with prefix V1_IP1 can bereached through an LSP to the V1-LER (M1) of mobile domain V1. So, itforward the packets to V1-LER (M1) via LSP2, using the appropriatelabels that enable the packet to travel from S11 to S12, from S12 to M2,and from M2 to M1, as indicated in the tables of FIG. 7 and shown inFIG. 10. Finally, the MLR function of V1-LER (M1) inspects the packetreceived via the LSP2 and it determines that the IP destination addressbelong to the local management subnet, so it routes the packet to theLAN 210.

Note that when said IP destination address corresponds to the address ofan on-board node like M2, the C1-LER (S11) can forward the packetdirectly to M2 (without passing via M1 as V1-LER), by accessing the FTNtable of C1-LER (S11) with FEC=F_M2. In this case, the packet is notprocessed by V1-LER's MLR function because it is not necessary.

In another example, the IP destination address belongs to the V1-IP2range. In this case, the MLR function of V1-LER will forward the packetvia a static route to the on-board gateway V1-GW, instead of sending itto the LAN 210.

As schematically shown in FIG. 11, for upstream traffic, i.e. from themobile domain V1 to the core network 10 or infrastructure network 100,the process is symmetric.

Note that, according to the tables of FIG. 6, on the V1-LER (M1), allnon-local prefixes not present in the MPLS FIBs are sent to the currentC1-LER (see FEC=default in the FTN(M1)). In turn, the C1-LER forwardsany unknown, non-locally connected mobile prefixes to the G-LER (seeFEC=default in the FTN(S11)). In this way, communications between mobiledomains Vi that are currently connected to different primary domains Cjare enabled through the G-LER.

For different mobile domains Vi connected to the same primary domain Cj,instead, the MLR of the local Cj-LER will re-route the traffic back viathe appropriate LSP of the same primary domain Cj. In this case, thetraffic stays within the same primary domain Cj and the G-LER is notinvolved, saving bandwidth and processing resources on the backbone andcore networks.

As clear from FIGS. 6 to 11, the mobility management method of thepresent disclosure enables to exploit and to let unchanged theintra-primary-domain/intra-mobile-domain LSPs predefined within eachprimary domain Vi and within each mobile domain Cj.

Changes of the network topology due to the relative motion between anymobile domain Vi with respect to primary domains Cj (that cause a localhandoff from a current couple of primary border node SB and mobileborder node MB into a new couple SB′-MB′, and optionally a globalhandoff as well) are handled only by changing the rows of the FIB tablesthat relate to the connection between nodes belonging to differentdomains.

At the bottom level, considering that connection between a primarydomain Cj and a mobile domain Vi is established by means of only onenode (the mobile border node MB/MB′) of the mobile domain Vi and onlyone node (the primary border node SB/SB′) of the primary domain Cj, asingle handoff procedure, involving a single one-hop label-switchedsegment (between the mobile border node MB/MB′ and the primary bordernode SB/SB′), is sufficient to provide complete connectivity amongst thelabel-switched nodes and the client devices of both domains. The numberof LSPs paths to be reconfigured at each local handoff procedure is thuslimited.

At the top level, at any global handoff procedure, the FIB tables of theG-LER remain unchanged apart from the rows of the FTN(G1) table relatingto the mobile domain Vi (last two rows with e.g. FEC=V1_IP1,FEC=V1_IP2), which need to be updated to connect to the current Cj-LER.On the other side, the FIB tables of the Cj-LER are updated to insert orcancel entries relating to the currently connected or disconnectedmobile domain Vi.

Accordingly, the local and global handoff procedures performed accordingto the present disclosure advantageously enable to significantly reducethe employment of node resources (e.g. memory usage, processing, numberof FIB table entries and number of updating operations on FIB tables),to limit the signalling and information spreading through the networkand the bandwidth usage, to improve the overall scalability of thesystem and contributes to provide very fast LSPs reconfiguration at eachhandoff procedure execution, reducing the chance to incur intotransmission errors.

Reconfiguration of the network can be thus performed very quickly (e.g.with latency in the order of few milliseconds) without servicedisruption and loss of data packets.

As clear from the above description, according to the presentdisclosure, packet communications between the Vi-LER and the Cj-LER (viathe primary border node SB/SB′ and the mobile border node MB/MB′) aswell as between the Cj-LER and the G-LER are established by means of twodisjoint label-switched paths. IP addresses of client devices of themobile domain Vi need not to be notified to nodes of the primary domainCj or to the G-LER. Client devices of the mobile domain Vi can thusmaintain the same IP address during mobility, preserving data packetsconnections intact.

In particular, from the label-switched network perspective, clientdevices of both the mobile domain Vi and the primary domain Cj maintaintheir reachability binding (that is they continue to be reachable)behind a same label-switched node during the entire lifetime of thesystem. The reconfiguration effects induced by mobility are completelymasked to all client devices by the FIB table modifications onlabel-switched nodes. Indeed, said FIB table modifications effectivelyavoid any changes in Layer-2 and Layer-3 reachability information storedacross the network about the client devices, as if the client deviceswere in fact mutually static.

According to the present disclosure, mobility management is performed bythe G-LER, Cj-LER, Vi-LER and the Nj label switched nodes of the Cjprimary domains, and the Mi label switched nodes of the Vi mobiledomains. The rest of the communication network 1, including the backbone400, the default gateway Core-GW of the core network 10 and the defaultgateway Cj-GW of the primary domains are not involved in handlingmobility management and communicate using standard IP routing. Mobilitymanagement according to the present disclosure can thus be implementedin a pre-existing network by installing and suitably configuring theG-LER, Cj-LER, Vi-LER and the Nj label switched nodes of the Cj primarydomains and the Mi label switched nodes of the Vi mobile domains,requiring no substantial changes to the rest of the communicationnetwork 1 and pre-existing devices (e.g. client devices, defaultgateways . . . ).

While there have been shown and described illustrative embodiments thatprovide for mobility management in a label switched network, it is to beunderstood that various other adaptations and modifications may be madewithin the spirit and scope of the embodiments herein. For example,while certain embodiments are described herein with respect to certainmobile domain deployment locations, such as trains, the techniquesherein are not limited as such and can be applied to any number ofmobile domains, in other embodiments. In addition, while certainprotocols are shown, other suitable protocols may be used, accordingly.

The foregoing description has been directed to specific embodiments. Itwill be apparent, however, that other variations and modifications maybe made to the described embodiments, with the attainment of some or allof their advantages. For instance, it is expressly contemplated that thecomponents and/or elements described herein can be implemented assoftware being stored on a tangible (non-transitory) computer-readablemedium (e.g., disks/CDs/RAM/EEPROM/etc.) having program instructionsexecuting on a computer, hardware, firmware, or a combination thereof.Accordingly, this description is to be taken only by way of example andnot to otherwise limit the scope of the embodiments herein. Therefore,it is the object of the appended claims to cover all such variations andmodifications as come within the true spirit and scope of theembodiments herein.

What is claimed is:
 1. A method comprising: receiving, at a gatewaylabel edge router, a packet destined for a mobile domain that comprisesa vehicle label edge router; identifying, by the gateway label edgerouter and from among a plurality of primary domains, a particularprimary domain that currently has a label switched connection with themobile domain, wherein the label switched connection connects thevehicle label edge router of the mobile domain and a cluster label edgerouter of the particular primary domain; sending, by the gateway labeledge router, the packet to the cluster label edge router of theparticular primary domain for transmission to the vehicle label edgerouter via the label switched connection; tracking, by the gateway labeledge router, when the vehicle label edge router of the mobile domainestablishes a new label switched connection with a second cluster labeledge router of a different primary domain in the plurality of primarydomains than that of the particular primary domain; and sending, by thegateway label edge router, an instruction to the cluster label edgerouter to delete information it has regarding the label switchedconnection that connected the vehicle label edge router and the clusterlabel edge router, after the vehicle label edge router establishes thenew label switched connection with the second cluster label edge router.2. The method as in claim 1, wherein tracking when the vehicle labeledge router of the mobile domain establishes a new label switchedconnection with a second cluster label edge router of a differentprimary domain in the plurality of primary domains than that of theparticular primary domain comprises: receiving an indication from thesecond cluster label edge router of the vehicle label edge routerestablishing the new label switched connection with the second clusterlabel edge router.
 3. The method as in claim 1, further comprising:receiving, at the gateway label edge router and from the cluster labeledge router of the particular primary domain, a second packet destinedfor the mobile domain, when the cluster label edge router of theparticular primary domain does not have a label switched connection withthe vehicle label edge router of the mobile domain.
 4. The method as inclaim 3, further comprising: identifying, by the gateway label edgerouter, the second cluster label edge router as currently having a labelswitched connection with the vehicle label edge router of the mobiledomain; and sending, by the gateway label edge router, the second packetto the second cluster label edge router for delivery to the mobiledomain.
 5. The method as in claim 1, further comprising: encapsulating,by the gateway label edge router, the packet into a Layer 2-over-Layer 3tunnel, prior to sending the packet to the cluster label edge router ofthe particular primary domain for transmission to the vehicle label edgerouter via the label switched connection.
 6. The method as in claim 1,wherein the particular primary domain comprises a plurality of nodes,and wherein the cluster label edge router of the particular primarydomain causes other nodes of the particular primary domain to updatetheir respective stores based on the instruction sent by the gatewaylabel edge router.
 7. The method as in claim 1, wherein the vehiclelabel edge router is located on a train.
 8. The method as in claim 1,wherein the mobile domain is assigned to a first Internet Protocol (IP)subnet and forms a first broadcast domain, and wherein the particularprimary domain is assigned to a second IP subnet and forms a secondbroadcast domain.
 9. The method as in claim 1, wherein the gateway labeledge router identifies, from among a plurality of primary domains, theparticular primary domain from a forwarding information base (FIB) tablemaintained by the gateway label edge router.
 10. An apparatus,comprising: one or more network interfaces; a processor coupled to theone or more network interfaces and configured to execute one or moreprocesses; and a memory configured to store a process that is executableby the processor, the process when executed configured to: receive apacket destined for a mobile domain that comprises a vehicle label edgerouter; identify, from among a plurality of primary domains, aparticular primary domain that currently has a label switched connectionwith the mobile domain, wherein the label switched connection connectsthe vehicle label edge router of the mobile domain and a cluster labeledge router of the particular primary domain; send the packet to thecluster label edge router of the particular primary domain fortransmission to the vehicle label edge router via the label switchedconnection; track when the vehicle label edge router of the mobiledomain establishes a new label switched connection with a second clusterlabel edge router of a different primary domain in the plurality ofprimary domains than that of the particular primary domain; and send aninstruction to the cluster label edge router to delete information ithas regarding the label switched connection that connected the vehiclelabel edge router and the cluster label edge router, after the vehiclelabel edge router establishes the new label switched connection with thesecond cluster label edge router.
 11. The apparatus as in claim 10,wherein the apparatus the apparatus is configured to track when thevehicle label edge router of the mobile domain establishes a new labelswitched connection with a second cluster label edge router of adifferent primary domain in the plurality of primary domains than thatof the particular primary domain by: receiving an indication from thesecond cluster label edge router of the vehicle label edge routerestablishing the new label switched connection with the second clusterlabel edge router.
 12. The apparatus as in claim 10, wherein the processwhen executed is further configured to: receive, from the cluster labeledge router of the particular primary domain, a second packet destinedfor the mobile domain, when the cluster label edge router of theparticular primary domain does not have a label switched connection withthe vehicle label edge router of the mobile domain.
 13. The apparatus asin claim 12, wherein the process when executed is further configured to:identify the second cluster label edge router as currently having alabel switched connection with the vehicle label edge router of themobile domain; and send the second packet to the second cluster labeledge router for delivery to the mobile domain.
 14. The apparatus as inclaim 10, wherein the process when executed is further configured to:encapsulate the packet into a Layer 2-over-Layer 3 tunnel, prior tosending the packet to the cluster label edge router of the particularprimary domain for transmission to the vehicle label edge router via thelabel switched connection.
 15. The apparatus as in claim 10, wherein theparticular primary domain comprises a plurality of nodes, and whereinthe cluster label edge router of the particular primary domain causesother nodes of the particular primary domain to update their respectivestores based on the instruction sent by the apparatus.
 16. The apparatusas in claim 10, wherein the vehicle label edge router is located on atrain.
 17. The apparatus as in claim 10, wherein the mobile domain isassigned to a first Internet Protocol (IP) subnet and forms a firstbroadcast domain, and wherein the particular primary domain is assignedto a second IP subnet and forms a second broadcast domain.
 18. Atangible, non-transitory, computer-readable medium storing programinstructions that cause a gateway label edge router to execute a processcomprising: receiving, at the gateway label edge router, a packetdestined for a mobile domain that comprises a vehicle label edge router;identifying, by the gateway label edge router and from among a pluralityof primary domains, a particular primary domain that currently has alabel switched connection with the mobile domain, wherein the labelswitched connection connects the vehicle label edge router of the mobiledomain and a cluster label edge router of the particular primary domain;sending, by the gateway label edge router, the packet to the clusterlabel edge router of the particular primary domain for transmission tothe vehicle label edge router via the label switched connection;tracking, by the gateway label edge router, when the vehicle label edgerouter of the mobile domain establishes a new label switched connectionwith a second cluster label edge router of a different primary domain inthe plurality of primary domains than that of the particular primarydomain; and sending, by the gateway label edge router, an instruction tothe cluster label edge router to delete information it has regarding thelabel switched connection that connected the vehicle label edge routerand the cluster label edge router, after the vehicle label edge routerestablishes the new label switched connection with the second clusterlabel edge router.